How Much Does It Cost to Run a Dehumidifier, a Fan, a Space Heater? Do the Sum Yourself

Short answer: one formula answers all of these, and it takes about fifteen seconds.

watts ÷ 1000 × hours × your rate per kWh = cost

At the US average residential rate of roughly $0.125 per kWh, a 300-watt dehumidifier running eight hours costs 30 cents. A 1500-watt space heater for the same eight hours costs $1.50. That is a five-fold difference, and it is entirely explained by the first number.

Every article answering this question quotes an average for an appliance that is not yours. Your appliance has its wattage printed on a plate on the back or underneath. Use that, and you will get an answer that is right rather than typical.

The three numbers you need

Watts. On the rating plate, in the manual, or on the box. If it lists amps instead, multiply amps by volts (120 in North America, 230 in the UK and most of Europe).

Hours. Actual running hours, which is the step almost everyone gets wrong — see the duty cycle section below.

Your rate. On your bill, in cents or pence per kWh. Not the national average, which can be off by a factor of two depending on where you live.

Typical wattages, as a starting point

Use these only until you can read your own label. Ranges are wide because these appliances genuinely vary that much.

The two rows people search for most are marked. Note the pattern: anything that makes heat is expensive, and anything that moves information is not. A fan costs pennies because it moves air. A heater costs pounds because it makes heat, and heat is the expensive thing electricity can do.

The step that makes every estimate wrong

Duty cycle. Most of these appliances do not run continuously even when switched on.

A dehumidifier runs its compressor until the target humidity is reached, then cycles. Over eight hours it might draw full power for three. A space heater with a thermostat does the same. A fan does not — it runs whenever it is on, which is why fan estimates are the reliable ones.

So for anything thermostatically controlled, the honest method is to multiply by a duty cycle:

This single correction is why your bill does not match the calculators. A dehumidifier maintaining a dry room costs roughly a quarter of what a naive eight-hour calculation predicts.

Consumer electronics account for 51% of idle load, miscellaneous electrical loads for 34%, and traditional large uses — heating, cooling, lighting and refrigeration combined — for just 15%.

Delforge, Schmidt and Schmidt, NRDC Home Idle Load, 2015

Your rate is not one number

The formula at the top uses a single rate per kWh. For a growing share of households that is no longer how the bill works, and the difference is large enough to change what you should do rather than merely what you pay.

Time-of-use tariffs charge different rates by hour. The spread between an overnight rate and a late-afternoon peak can be a factor of three or more. Under one of these, when you run the dehumidifier matters as much as whether you do.

Tiered rates charge more per unit once you pass a monthly threshold. Under tiering, the marginal cost of the last appliance you switch on is higher than your average rate, so a calculation using the average understates it.

Standing charges are fixed daily fees that do not vary with use. They are not affected by anything in this article, and they are why cutting consumption by 20% rarely cuts the bill by 20%.

To find which you are on, look at the supply rate section of your bill rather than the total. Then:

The order to work through your own home

If you want to do this properly rather than satisfy a single curiosity, work top-down.

1. Get your actual rate from the bill. Everything downstream is wrong without it.

2. Read the meter last thing at night and first thing in the morning. The difference over a period when nothing should be running is your idle load. Compare against the 164-watt average.

3. List anything that runs continuously. Fridge, freezer, router, set-top box, pond or aquarium pump, hot water recirculation, security system. These are cheap per hour and expensive per year, and they are where the surprises live.

4. List anything that makes heat. Heaters, kettle, oven, dryer, hot tub, immersion heater. These are expensive per hour and usually cheap per year because they run briefly — except when they do not, which is the hot tub.

5. Measure the two or three you are least sure about with a plug meter.

Almost everyone doing this finds the same thing: the appliance they were researching costs very little, and something they never considered costs a lot.

Measure instead of estimating

A plug-in energy monitor costs about the price of a takeaway and removes all of the above guesswork. Plug it in, leave the appliance running a normal day, read the kWh total. That number includes the duty cycle automatically, because it measured what actually happened.

This is the same tool recommended in our piece on whether unplugging appliances saves electricity, and it answers both questions at once: what things cost while running, and what they cost while doing nothing.

The costs worth your attention

Working out what a fan costs is satisfying and financially irrelevant. Here is where the money actually is, and it is not on the list people search for.

Heating and cooling. Nothing else is close in most homes. A space heater used as primary heating for one room is often more expensive than central heating for the whole house, because electric resistance heat is the least efficient way to buy warmth.

Anything with a compressor running continuously. Fridges, freezers, dehumidifiers in damp homes, hot tubs. Low wattage but 24 hours a day, which is the same arithmetic problem as idle load.

The always-on background. The NRDC's audits across 70,000 homes found idle devices accounted for around 23% of household electricity, averaging 164 watts of continuous draw and roughly $165 a year. That is more than most of the individual appliances people research.

Not the fan, the LED bulb or the phone charger. A fan running every night all summer costs a few dollars for the season.

Quick answers to the exact questions people ask

A dehumidifier: 250–700 W. At 40% duty cycle for 8 hours, about $0.12–$0.35 a day, more in a genuinely damp room. Modern units are considerably better than ten-year-old ones.

A fan all night: 40–100 W for 8 hours, roughly $0.04–$0.10. Cheaper than almost any alternative for feeling cooler, because it cools you rather than the room.

A space heater: almost always 1500 W at maximum. At full output, about $0.19 an hour. All 1500 W heaters produce identical heat regardless of price or technology — infrared, ceramic, oil-filled — because they are all converting the same electricity into the same energy. Anything claiming otherwise is claiming to break physics.

A ceiling fan: 15–90 W, so $0.02–$0.09 for 8 hours. Turn it off when you leave the room; it cools people, not air.

A hot tub: the outlier. Heater plus circulation pump running daily puts most hot tubs in the $30–$100 a month range depending on climate, insulation and cover quality. The cover matters more than anything else you can change.

Electricity rates vary widely by region, tariff and time of day. All costs here use the US average residential rate of about $0.125/kWh; check your own bill and scale proportionally.